Don't fly to Rendezvous region when "Launch mission" button is pressed

[copyrite]

When the "Launch mission" button is pressed, Avenger lifts off and lands in the region where the Rendezvous takes place. This is consistent with how other missions behave: Avenger must fly to the region to send the infiltrating or quick responding squad. However, fluff-wise the squad is already on the mission site, so that doesn't apply, and Avenger is not required to move to the region to evac the squad either. Therefore an exception should be made to the UI that the Rendezvous mission would start without the flight, which wastes both strategic and player time.